(a) Field of the Invention
This invention relates to a hip prosthesis. More particularly, the invention is concerned with a hip prosthesis of the type that is designed to prevent unlocking thereof after surgery.
(b) Description of the Prior Art
In spite of the fact that there are many available hip prostheses that can be used to replace damaged hip joints, one is often faced with the problem that hip prostheses are sometimes subject to unlocking after surgery, either because the acetabulum part is not sufficiently fixed into the acetabulum or the femur part which is inserted in the femur canal is not sufficiently anchored therein. This is of course a serious problem, since if this should happen, a new surgery may have to be undertaken, and possibly a new hip prosthesis may have to be installed.
In order to overcome the above disadvantages, there is provided a hip prosthesis to replace a damaged hip-joint, the hip prosthesis to be disposed at one end thereof into a cup-shaped cavity of an acetabulum and at the other end thereof into a femur canal of a person suffering from a damaged hip-joint. The hip prosthesis comprises
an acetabulum part comprising a cotyloid member and means for tightly engaging the cotyloid member into the acetabulum;
an elongated neck part;
a femur part;
the elongated neck part having an articulation head at one end thereon, the head being shaped to be articulately received in the acetabulum part, and slidable connecting means at the other end thereof for engagement with the femur part;
the femur part having a femur canal insertable portion formed with means to secure same in the femur canal by being embedded in regenerated bone marrow, and engaging means to receive the slidable connecting means of the elongated neck part and to securely connect the elongated neck part to the femur part.
The acetabulum part is preferably semi-spherical, and may be provided with a plurality of peripheral flanges capable of engaging with the acetabulum.
In accordance with a preferred embodiment, the peripheral flanges are each formed with a plurality of outwardly projecting points which may be regularly distributed along each flange, each projecting point forming an angle of between about 30 and 60xc2x0, preferably about 45xc2x0 with respect to a tangent at the location of a respective projection point. Preferably, the projection points are oriented in a way to be engaged within the acetabulum when rotating the acetabulum part clockwise.
In accordance with yet another embodiment, the hip prosthesis according to the invention comprises a buffer member adapted to be fixedly mounted inside the acetabulum part, and to snappingly engage the articulated head. The buffer part is preferably semi-spherical, and provided with a cup-shaped cavity to receive the articulated head. It may be made of an inert material such as polyethylene, ceramic and an inert metallic substance. On the other hand, the preferred material of the acetabulum member is a titanium containing substance.
In accordance with yet another embodiment, the slidable connecting means of the elongated neck part comprises an inverted T-shaped portion which is perpendicular to the neck part, and the engaging means of the femur part comprises a slide member formed with an inverted T-shaped channel shaped to slidably receive the inverted T-shaped portion. The inverted T-shaped portion and the sliding member are normally adapted to be secured together by means of screws.
In accordance with yet another preferred embodiment, the femur part comprises a rectangular shaped shank portion joining the femur canal insertable portion and the slide member.
Preferably, the femur canal insertable portion comprises a first elongated pyramidal member extending from the shank portion, an elongated trapezoidal member shorter and narrower than first elongated trapezoidal member and projecting from first elongated pyramidal member, and a second elongated pyramidal member shorter and narrower than the trapezoidal member and tapering down from the shank portion to the opposite end thereon, the femur canal insertable portion thereby easily being embedded in the regenerated bone marrow.
In accordance with yet another embodiment, femur canal insertable portion angularly extends from the shank portion and the sliding member, for example the femur canal insertable portion extends from the shank portion at an angle of about 15xc2x0 and from said sliding member at an angle of about 45xc2x0.
In accordance with yet another embodiment, the acetabulum part comprises a hollow truncated half sphere having a flat face, triangular openings being formed in the flat face to permit growth of bone cells into the hollow truncated half sphere, and screw holes along the lower edge of the hollow truncated half sphere oriented at about 45xc2x0. In this case, the buffer member is preferably spaced from the walls of the hollow truncated half sphere wherein bone cells can be permitted to grow.